This invention relates generally to gas turbine engines having adjustable stator vane assemblies and in particular to an improved actuation system for effecting vane adjustment.
Gas turbine engines employing axial compressor structures typically embody longitudinally spaced high and low pressure compressor sections each having a plurality of stator vane stages wherein means are provided for varying the positions of the stator vanes in selected stages relative to the engine casing. In one common arrangement, each stator vane in a stage has a shaft rotatably supported on and projecting out of the engine casing. Each shaft, in turn, has an actuator arm attached to it and the ends of all of the arms for the particular stage of vanes engage an actuator ring disposed around the engine. Driving means are provided between a fixed support, such as the engine casing, and the ring to effect rotation of the ring and consequent pivotal movement of each actuator arm for simultaneously adjusting the positions of the vanes. When it is desired to adjust more than one stage of vanes there is usually provided a common actuating device, such as a push rod, which functions to simultaneously drive each of the actuator rings. Once adjustment is achieved, the driving means and the actuator rings function to rigidly maintain the individual stator vanes in their adjusted positions.
Where the adjustable stages are located in longitudinally spaced compressor sections, significant operating temperature differences are usually encountered which cause the engine casing and other components to exhibit different thermal growth patterns at the longitudinally spaced stator vane stages. If means are not otherwise provided, the different thermal growth patterns can change the adjusted positions of the vanes, thus effecting engine performance, or can impose undesired loads on bearings and bushings, making adjustment more difficult. A vane actuation system according to this invention represents an improvement over heretofore known systems for effecting simultaneous adjustment of stator vanes disposed in different temperature environments.